Load division trim control by interconnected sensing devices



July 23, 1957 s. H. FAIRWEATHER UAL 2,800,593

LOAD DIVISION TRIM CONTROL BY INIDROONNEOIDD sENsINO DEVICES Filed July l5, 1954 n Kur LS'e/dzzer United States Patent" Oilice Lon' nrylsro'N TRM CONTROL BYrNTER- CONNECTED SENSING DEVICES sfephsanFirweangsputh Euclid, william L. nitide,

Euclid,fandKurt Seidner, Mayfield Heights, Ohio, sig'nors to'. Thompson Products, Inc., Cleveland, Ohio, a corporation of Ohio Abpxicatinruly 1s, 19354,'seria1 No. 442,936

, lllClains. (Cl.30757) Thepresentwinvention*relates `toyload division trim control-by interconnected sensing devices, and more particularly) relates to a system forcontrolling` load division between paralleled alternators by interconnecting devices sensing` operating conditions 'of theI altenators. v t

Still more particularly, theinvention relates to a system for'interconnecting" control means such as that described'` in y'the application for UnitedStates Letters Patent entitle'dffControl System For Turbine Driven Alternators, by v Walter R Chapman and Stephen H. Fairweather, United States-Serial `No. 382,582, led September 28, 1953, to ,provide means yto compensate for variations between the level ofthe two loads on each of the alternators thealternators are connected in parallel to a common lc'ia'd.:v4 I y l A lndeliectrical power installations, Yandparticularly in alternating current electrical power installations it has been 'found'r tobe highlydesirable practice from a point of view .of economyand eiciency, to supply electrical power tofthe'load generally 'by oneV ormore of a plurality of a1ternator'swlfiich'rnay.V beconnec'ted in parallel. This parallelconnection of a plurality of alternators is desirahlesincecnly one su'ch alternator need bev employed whent supplyingy power to a 'small load while two, three or four alternators maybe connected to the main power supplylinefor. supplyingpower to relatively large loads.

Whennparallelalternatorsare employed, however, it is mostv important that the load be divided substantially equally.therebetweemwhen the alternators are of substantially egual capacity, and thatfthe. alternators be operatedfin'phaseand at'substantially the 'same speed, since to do otherwise would result Iinv a tendency for one'or more of the alternators to assume substantially'allof the load and thereby be overloaded while other of the alternators would tend to give up their load and therebyrun as motors. Such mal-operation is obviously detrimental and undesirable.

In the above identified application for patent by Walter R. Chapman and Stephen H. Fairweather there is described a system for controlling the speed and power input to each of a plurality of alternators so that the droop characteristic thereof will be accurately controlledhand when a plurality vof alternators using' such controls are paralleled, they will have substantially identical droop characteristics. By having very similar` or substantially identicaldroop characteristics the alternatorswill tend tooperate in a parallel system with substantially equal load divisions therebetween. y, v v

One of the principal and mostimportant features of the present invention lies in the provisionl of a system ofinterconnecting the system describedin the hereinabove identified application so as to insure proper load` division between alternators when the same areinterconnected and operating as controlled bythe `transducer and control systems described in the above' identifed'application.

In that transducer control system, each transducer has real load sensing means therein lconnected to the alternator which" it controls so' that onel ofithe parameters whichA actuates the transduceris a real load sensing signal. This signal together'with a signal from a speed sensing network, and other signals control the alternator drive, and more particularly the input speed and power to the alternator drive so that when the alternatorshouldassume a greater portion of the load or when `a greater load is thrown on the alternator, the input drive power will be increased to bring the alternator back to its set speed or to a preselected level therebelovv depending upon the controllable desired droop characteristic for the alternator.

Although the manner of detail operation of the transducer control system forms noi part of the present invention, it hasbeen described in thevabo've identified application as having particular utility in aircraft installations and is particularly adaptableifor controlling pneumatic driven turbines coupled tothe alternators for driving the alternators. Its particular applicability and adaptability to aircraft installations is enhanced by the compactness of the unit and the lightweight of the total package.

So too, the system of the present invention is particularly adaptable to such an aircraft pneumatic-electric power system since it adds substantially no weight tothe entire system and does not enlargethe bulk of the system.

l In accordance with the principles of the present invention the load sensing network of 'each of thetransducers for the several alternators to be connected in parallel may be connected together on the input sides thereof in series so that unbalances betweenthe" real load sensing signals thereto maybe corrected and the alternators may be operated isochronously. More particularly,`the real load sensing networks of the transducer control systems maybe coupled to the alternators respectively by a current trans*- former, or equivalent means, which will provide a current `sensing signal' to the real load sensing network, andl by a potential lead connected'to one of the output leads of the respective alternator. As'hereinafter described in detail, the trim control inter-connection ofthe transducers maybe effected by interconnecting the outputs of the current transformers in series so'that unbalances therebetween will result in variations ofthe signals provided to the reel load sensing networks so that the transducers will be actuated to control the drive'for the individual alternators in such a manner that thealternators will be operated isochronously with substantiallyy equal loads thereon, or with' the common load substantially equally divided therebetween.

Numerous other'object's,` features and advantages of the present invention willvbecomeY readily apparent to those skilledin the'v art from the, following detail description of the present inventionv and from the accompanying drawing'in which each and every detail shown is fully and completely disclosed as a part'of this specilication,l and in which there is schematically illustrated an embodiment of Ithe present invention.`

Although any desired pluralityofV alternators may be operated together iny parallel to supply power to a load, iu' lthefsystem illustrated on the drawings four such altern atorsQlO, v11,12 and as indicated at 14, 15, V16 and 17 have been shown. Each ofthesejalternatorshas three power leads (the A, B 4and C phases-thereof), 10a, 10b'and10c`, 11a 11b and llc 12a,

12b and 12e, 13a, 13b an-d 13e, respectively. The A leads are connectedto the: A but 18a, while the B leads are" connectedto the Ybus 18b and the C leads are connectedto the bus 18`c, the busses in turn being connected'to th'ecommon load 19 which may have a grounded vpoint such as indicated at 20.

Thealternators mayY be driven by a pneumatic turbine or the like through a gear box, with the turbine being supplied-with lairpowerthrough a supply line and being controlledr'by a transducer' control systemY which is Vcou- Patented July 23, 1957 13 of the grounded neutral type pled to the output of the individual alternators. For simplicity of illustration and description, only one such supply line, turbine and transducer has been shown in the proper interconnected relation on the drawings, it being understood that the transducers and turbines, etc., for the other alternators are substantially identical to the one illustrated and described.

Therefore, as shown, the alternator 10 is driven by a pneumatic turbine and gear box indicated schematically at 21 and supplied with air power through a supply line 22. The turbine and supply lines are coupled, as indicated by the broken mechanical coupling lines 23, 24 and 25 to the output of a transducer control system 26 such as described in the hereinabove identified application. The alternator is coupled to the turbine and gear box as indicated by the broken mechanical coupling line 27. Also coupled to the output of the pneumatic turbine and gear box is a speed sensing unit such as a tachometer generator 2d which is mechanically coupled as indicated by the broken mechanical coupling line 29 and which has an output the frequency of which is directly related to the speed of the alternator. The output of the tachometer generator 28 is taken over leads :ttl-30 to an appropriate pair of terminals 31-31 on the transducer control system 26 and there fed into the transducer control system.

The broken arrows 26a, 27b and 27e on the alternators 11, 12 and 13 indicate that those alternators will be driven in substantially the same manner in which the alternator 1) is driven and controlled.

In addition to a speed sensing signal from the tachometer generator 28, the transducer 26 is also supplied with load sensing signals including a current sensing signal supplied thereto from the output of a current transformer 32 on the output lead 10a of the alternator 1d. This current sensing signal is fed to the transducer control system over leads 33-33 to appropriate terminals 34-34 on the transducer control system which lead to appropriate terminals .3S-35 on a real load sensing network schematically indicated at 36. Also, a potential carrying lead 37 is connected to the alternator lead 10a at one end thereof and to an appropriate terminal 38 on the transducer control system and from the terminal 3S through a lead 39 to an appropriate terminal 40 in the real load sensing network 36.

In a like manner, current sensing means such as the current transformers 32a, 321'; and 32C are coupled to the alternator output leads 11a, 12a and 13a, respectively, and are connected through leads 33o-33a, 33b-33b and 33e-33o to appropriate terminals 34a-34a, 34b- 34b and 34e-34C on the transducer control systems 26a-26b-26c and to the real load sensing networks therein. Also, potential sensing leads 37a-37b and 37e are respectively connected to the leads 11a, 12a and 13a and to the transducer control systems 26a, 26b and 26C and therein to the respective real load sensing networks.

With the alternators thus driven and connected to their respective transducer control systems, each thereof will have a predetermined and manufactured droop characteristic which will be controlled in accordance with the settings in the transducer control system, the transducer control system being operative in accordance with signals provided thereto and in accordance with the operating parameters of the alternators. When still operating the load on each of the alternators will be divided substantially equally so long as the droop characteristics thereof are substantially identical. Because of various factors which are inherent in the systems, however, and various other transient factors, these systems may tend to go into an unbalanced condition which will bey aggravated by the natural operating characteristics of the alternators. Therefore, an important feature of the system herein described lies in inter-connecting the control systems so that variations between the loads thereon will be corrected and the alternators will operate isochronously and with the loads substantially equally divided therebetween. One manner of inter-connecting the control systems is to connect the outputs of the current transformers 32, 32a, 3211 and 32o in series as by leads 41, 42 43 and 44. These leads are so connected into the system that one end of the lead 41 is connected at one of its ends to one of the leads 33 while the other end thereof is connected to one of the leads 33C, while the lead 42 has one of its ends connected to the other of the leads 33e and to one of the leads 33b, the lead 43 having one of its ends connected to the other of the leads 33h and to one of the leads 33a and with the lead 44 having its ends connected to the other of the leads 33H and to the other of the leads 33.

With these leads connected into the system in the described manner, unequal outputs in the current transformers 32, 32a, 32b and 32c, resulting in unequal inputs to the transducers 26, 26a, 26h and 26C and the load sensing networks 4) therein, will result in appropriate variations in the input to the transducers to correct and compensate for variations between the loads on the alternators 10, 11, 12 and 13. That is an example, if the load on the alternator 1t) is too great, then the leads 41, 42, 43 and 44 will carry appropriate signals to the load sensing systems in the transducer control systems 26a, ab and 26C to cause the alternators 11, 12 and 13 to carry an increased share of the load until the load is divided substantially equally between the alternators and the alternators carry substantially equal loads.

Since the alternators are not always all used at the same time, means has been provided for cutting the con-4 trol elernents thereof out of the control system. Such means includes short circuiting switches 4S, 46, 47 and which are connected across the outputs of the current transformers 32, 32a, 32!) and 32e, respectively. It will be understood, of course, that the short circuiting switches or circuit breaker contacts are open while the respective alternators are connected together in parallel and are closed for short circuiting the respective current transformers when the respective alternators are out of the system. Appropriate means such as switches and indicator devices (not shown) may be employed to connect and disconnect the alternator power leads from the busses.

In addition, means such as a switch 49 in the line 41 may be employed to open the line and thereby open the interconnection between the alternator controls when it is desired to use only one ofthe alternators to supply power to the load 19.

lt will be understood that numerous variations and modifications may be made .vithout departing from the true spirit and scope of the novel concepts and principles of our invention.

We, therefore, intend to cover all such modifications and variations as fall within the true spirit and scope of the novel concepts and principles of our invention.

We claim as our invention:

l. A system to substantially equally divide a load between parallel interconnected alternators and to cause the same to operate isochronously wherein the input speed and power of the alternators is controlled by a transducer control system for each of the alternators respectively,

. each of said transducer control systems having means therein to sense the load on the alternator controlled thereby respectively, and means interconnecting the load sensing means of said transducer control systems whereby variations between the loads on the individual alternators will be corrected and the alternators will be operated isochronously with equal loads thereon.

2. A. system to substantially equally divide a load between parallel interconnected alternators and to cause the same to operate isochronously wherein, the input speed and power of the alternators is controlled by a transducer control system for each of t ealternators respectively,

sodass each of said transducer control systems having means therein to scuse the load on the alternator controlled thereby respectively, and means interconnecting the load sensing means of said transducer control system in series whereby variations between the loads on the individual alternators will be corrected and the alternators will be operated isochronously with equal loads thereon,

3. A system to substantially equally divide a load between parallel interconnected alternators and to cause the same to operate isochronously wherein, the input speed and power of the alternators is controlled by a transducer control system for each of the alternators respectr 1 each of said transducer control systems having r -ns therein to sense the load on the alternator controlled there by respectively, and means interconnecting the load sensing means of said transducer control syste-n1 in series at the input side thereof whereby vari ions between the loads on the individual alt -rnators v ill be corrected t the alternators will be operated isochronously with loads thereon.

4. A system to substantially equally divide a load between parallel interconnected alternators and to cause the same to operate isochronously wherein, the input speed and power of the alternators is controlled by a transducer control system for each of the alternators respectively, each of said transducer control systems havinfy means therein to sense the load on the alternator controlled thereby respectively, each of said load sensing means having alternator current sensing means and alternator potential sensing means, said current sensing means being connected together whereby variations between the loads on the individual alternators will be corrected and the alternators will be operated isochronously with equal loads thereon.

5. A system to substantially equally divide a load between parallel interconnected alternators and to cause the same to operate isochronously wherein, the input speed and power of the alternators is controlled by a transducer control system for each of the alternators respectively, each of said transducer control systems having means therein to sense the load on the alternator controlled thereby respectively, each of said load sensing means having alternator current sensin 7 means and alternator potential sensing means, said current sensing means being connected together in series whereby variations between the loads on the individual alternators will be corrected and the alternators will be operated isochronously with equal loads thereon.

6. A system to substantially equally divide a load between parallel interconnected alternators and to cause the same to operate isochronously wherein the input speed and power of the alternators is controlled by a transducer control system for each of the alternators respectively, each of said transducer control systems having means therein to sense the load on the alternator controlled thereby respectively, each of said load sensing means having alternator current sensing means and alternator potential sensing means, said current sensing means being connected together whereby variations between the loads on the individual alternators will be corrected (i and the alternators will be operated isochronously with equal loads thereon, and means connected to each of said current sensing means to short circuit the when the respective alternator is disconnected from the others and not in use.

7. A system to substantially equally divide a load between parallel inter-connected alternators and to cause the same to operate isochronously wherein the input speed and power of the alternators is controlled by a transducer control system for each of the alternators respectively, said transducer control system being connected together by means inter-connecting the load sensing means of said transducer control systems whereby variations between the loads on the individual alternators will be corrected and the alternators will be operated isochronously with equal loads thereon.

8. A system to substantially equally divide a load between parallel inter-connected alternators and to cause the same to operate isochronously wherein the input speed and power of the alternators is controlled by a transducer control system for each of the alternators respectively, said transducer control systems being connected together by means interconnecting the load sening means of said transducer control systems in series whereby variations between the loads on the individual alternators will be corrected and the alternators will be operated isochronously with equal loads thereon.

9. A system to substantially equally divide a load oetween parallel inter-connected alternators and to cause the same to operate isochronously wherein the input speed and power of the alternators is controlled by a transducer control system for each of the alternators respectively, means to supply input signals to said transducer control systems in accordance with operating parameters of the alternators respectively, said means being connected together by means inter-connecting the sensing means of said transducer control systems whereby variations between the loads on the individual alternators will be corrected and the alternators will be operated ischoronously with equal loads thereon.

10. A system to substantially equally divide a load between parallel inter-connected alternators and to cause the same to operate isochronously wherein the input speed and power of the alternators is controlled by a transducer (control system for each of the alternators respectively, means to supply input signals to said transducer control systems in accordance with operating parameters of the alternators respectively, said means being connected together by means inter-connecting the sensing means of said transducer control systems in series whereby variations between the loads on the individual alternators will be corrected and the alternators will be operated isochronously with equal loads thereon.

References Cited in the le of this patent UNITED STATES PATENTS 

